1. Field
Example embodiments generally relate to telecommunications networks, methods of assigning scrambling codes therein, methods of utilizing scrambling codes therein, and methods of reducing interference within telecommunications networks.
2. Description of Related Art
FIG. 1 illustrates a portion of a conventional wireless telecommunications system. As shown, the telecommunications system includes a base station 10 and a plurality of mobile stations 15A-15C. As discussed herein, one or more of mobile stations 15A-15C may be referred to herein as mobile station(s) 15. In FIG. 1, each mobile station 15A, 15B, and 15C is associated with a respective code tree A, B and C.
Various types of signals are transmitted between base station 10 and individual mobile stations 15 associated therewith, including both user content/traffic and control-type overhead signals used for communicating.
At the base station 10, signals transmitted on the downlink (e.g., from base station 10 to mobile station 15) are spread and scrambled with a code known to both the base station 10 and the mobile station 15. Different spreading and scrambling codes may be used with different mobile stations and different types of signals to enable the mobile stations 15 to differentiate among types and ownership of received signals.
As mentioned above, reference to mobile station 15 refers to one or more of mobile stations 15A, 15B and 15C. Similarly, reference to signals 20 refers to one or more of signals 20A, 20B and 20C. Similar references to other components/signals throughout this discussion should be interpreted similarly.
Still referring to FIG. 1, at the base station 10, in of each code trees A, B and C an encoder/multiplier 11 encodes/spreads the user content/traffic signals 20 with a first spreading code W1. User content/traffic signals 20 include, for example, voice data, short messaging service (SMS) messages, streaming video, etc. Another encoder/multiplier 11 encodes/spreads the overhead signals 21 with a second spreading code W2. Overhead signals 21 include, for example, pilot signals, pages, synchronization messages, etc. Other overhead signals 22 are encoded with a third spreading code W3 by another encoder/multiplier 11.
Each of Code Trees A, B, and C is associated with a unique set of signals 20-22 that are simultaneously or otherwise transmitted to mobile stations 15. Signals from different code tree sets may be generated for, and ultimately transmitted to, a single mobile station. For example, a single mobile station 15A may be associated with distinct signals 20A, 20B, and 20C from three different code trees. Although only 3 different signals 20, 21, and 22 and 3 different mobile stations 15A, 15B, and 15C are shown in FIG. 1, many more signal types and mobile stations may be present in conventional wireless networks.
Still referring to FIG. 1, on each of code trees A, B and C, respective groups of encoded signals 20, 21 or 22 are superimposed or summed by code-tree specific summing device 12. The resultant summed signals for a particular code tree are then scrambled with additional code-tree specific scrambling codes PNA, PNB, PNC at a respective scrambler/multiplier 13 before being transmitted to mobile stations 15.
With respect to code tree A, for example, code-tree specific summing device 12 sums traffic signals 20A and overhead signals 21A and 22A. Scrambler/multiplier 13 then scrambles the resultant signal with scrambling code PNA.
As shown in FIG. 1, once all coding is complete, a scalar multiplier 19 adjusts the average power for each signal set. In one example, the multiplier 19 adjusts the average power for a particular user and/or signal semi-statically (e.g., every several seconds) to match the load of the code resource to an optimized composite signal power. A base-station specific summer 14 superimposes or sums all signals from base station 10 and transmits the signals to mobile stations 15 on one or more frequencies associated with base station 10.
Spreading codes W1, W2, and W3, code tree-specific scrambling codes PNA, PNB, PNC, and/or identifiers thereof are transmitted to individual mobile stations 15 on an overhead channel designated for code reception. As a result, the mobile stations 15 possess the individual codes to decode received signals. Further, individual spreading and scrambling codes may be set by standards governing the operation of wireless networks such that mobile stations 15 know what spreading and scrambling codes correlate to what type of signal and to which user. Because the spreading and scrambling codes are known to the mobile station 15 and because the spreading and scrambling codes are distinct for each type of signal and code tree the mobile stations 15 are able to identify the type and ownership of the signals 20, 21, and 22. In addition, the mobile stations 15 are able to properly decode and utilize the information carried by the signals.
Similarly, mobile stations 15 ignore signals encoded with other or unknown spreading or scrambling codes. In this way, several different types of data may be transmitted and received on the downlink from several base stations to mobile stations.
One known type of spreading code is a Walsh code. Walsh codes are binary codes several-digits in length. Each Walsh code may be entirely or substantially uncorrelated, or orthogonal, to each other Walsh code used by a particular base station 10 such that different signals encoded with different Walsh codes are readily distinguishable. The following example sequences illustrate a code set of length 4 Walsh codes, all of which are orthogonal to each other:W1={1,−1,1,−1};W2={1,1,1,1};W3={1,1,−1,−1};W4={−1,1,1,−1}
An example of a known type of scrambling code is a Pseudo-Random Noise (PN) code. PN codes are binary or complex. And, signals encoded with PN codes are perceived as random background noise by mobile devices using different PN codes. Each PN code may be entirely or substantially uncorrelated, or orthogonal to each other PN code used by a particular base station 10.
In conventional networks with thousands of individual users, lengthy PN codes (e.g., having lengths of 215) are used to provide a unique set of codes for each type of transmission to each user. Some codes are similar or used in a similar order for specific types of overhead signals among mobile stations 15 and base stations 10. But, each mobile station 15 and base station 10 uses an offset that uniquely phase-shifts each code resource set, which includes the spreading and scrambling codes for all signals directed to a particular code tree. The unique phase shift reduces the possibility of a transmission from one base station 10 being misinterpreted as a multi-path transmission from another base station.
Further, users in a “soft handoff” zone (e.g., moving between geographical locations serviced by multiple base stations 10) may receive data simultaneously or concurrently from multiple base stations. This requires allocation of a unique PN code set from each one of those base stations for a single user. Thus, it is possible for a single user to be assigned multiple code resource sets, or subsets thereof.